An electronic control for a diesel engine may have a speed governor that embodies closed-loop control of engine speed. The closed-loop control may include proportion, integral, and derivative (sometimes referred to as PID) functions. When an engine speed request is less than a low idle speed set-point defined by a set-point table, the control is effective to maintain speed substantially at that setpoint by clamping the integral function in accordance with a calibratable limit. The inclusion of such an integral clamping function has an effect on the PID control when the speed command is not below the low idle speed set-point, and for certain conditions, may prevent the integral term from contributing to engine speed governing in an optimal manner for such conditions. An example of one such condition is a change in the speed request that calls for engine acceleration where continued wind-up of the integral term is desirable. The presence of the clamping function may impair wind-up of the integral term in a way that affects the ability of the engine to accElerate in an optimal manner.
Moreover, when an engine is running at or near its low idle speed set-point, it may for any of various reasons experience under-running, meaning that the engine speed actually drops below the low idle speed set-point. Should the engine be unable to recover fast enough, the speed may drop sufficiently to cause the engine to stall. Stalling may be somewhat unpredictable, and possibly attributable to the effect of certain factors inherent in the mass production of engines and/or of components in a drivetrain which is coupled to the engine. For example, if a drivetrain is slightly less efficient than the norm, yet still within acceptable tolerance, and if the engine is delivering less torque than the norm, yet still within acceptable tolerance, a combination of the two, even though improbable in any given mass-produced vehicle, may occur in some vehicles and render the engine prone to stalling should the speed drop below the low idle speed set-point. Statistical probabilities applied to mass production of manufactured components suggest that the probability of any particular vehicle having such a combination is sufficiently low that raising the low idle speed setpoint for all engines, which would needlessly waste fuel when the engines are idling and might have implications on tailpipe emission levels, would be an inefficient solution. Yet, the occurrence of the condition in a vehicle could lead to dissatisfaction for the customer involved if repeated stalling were to occur.
One solution to the problem would be to readjust the engine calibration by supplying an excess of fuel, but that solution may be unacceptable because of adverse impact on tailpipe emissions. Accordingly, it is believed that a better solution would guard against such an event without penalizing idle fuel consumption of all vehicles and without adverse tailpipe emission implications would be useful. Moreover, a solution that would be especially cost-effective would be even more desirable.
It is toward such a solution that the present invention is directed.
One general aspect of the invention relates to an engine speed governor of a diesel engine in a motor vehicle having a driveline that can be selectively engaged with and disengaged from the engine. The speed governor comprises an engine control comprising a processor for processing data for engine speed governing, including developing fuel request data comprising data components derived from proportional, integral, and derivative processing of difference between actual engine speed and requested engine speed. A data source distinguishes between engagement and disengagement of the driveline with and from the engine. A first table is associated with at least one of the proportional, integral, and derivative processing and provides selectable calibration values used by the processor during that processing to develop the fuel request data when the data source for distinguishing between engagement and disengagement of the driveline with and from the engine indicates engagement of the driveline with the engine. A second table is associated with the at least one of the proportional, integral, and derivative processing and provides selectable calibration values used by the processor during that processing to develop the fuel request data when the data source for distinguishing between engagement and disengagement of the driveline with and from the engine indicates disengagement of the driveline from the engine.
Another general aspect of the invention relates to an engine speed governor for a diesel engine including a load that can be selectively engaged with and disengaged from the engine. The governor comprises a processor for processing data for engine speed governing, including developing fuel request data comprising data components derived from proportional and integral processing of difference between actual engine speed and requested engine speed. A data source distinguishes between engagement and disengagement of the load with and from the engine. A first table associated with at least one of the proportional and integral processing provides selectable calibration values used by the processor during that processing to develop the fuel request data when the data source for distinguishing between engagement and disengagement of the load with and from the engine indicates engagement of the load with the engine. A second table associated with the at least one of the proportional and integral processing provides selectable calibration values used by the processor during that processing to develop the fuel request data when the data source for distinguishing between engagement and disengagement of the driveline with and from the engine indicates disengagement of the load from the engine.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. The disclosure includes drawings, as now briefly described.